Reinforced Downtubes and Toptubes

Independent Fabrications' touring bikes have been built with reinforced downtubes. The designer said that he had seen too many frame failures on the downtube, near the juncture with the head tube -- he had seen this enough times to warrant reinforcing the area. The top tube is also reinforced near the headtube.

A recent thread on bikeforums.net dealt with a failure after hitting a pothole, with good pictures of the damage, and the repair job as well: Potholed, is my LHT still rideable?

Another advantage of the Independence frames is that they can be built from Reynolds 853 and other hardened steels (the fork is also made from stronger-than-usual steel). These steels have far higher yield strengths than the usual, non-hardened steels (and some of the other materials) used in most touring bikes.

What other bikes are made of tubing or materials that are significantly less likely to fail? -- especially in collisions with curbs, potholes, rocks, and other objects that cause these sorts of damage and failures?

Yeah, most of us saw that thread. If you noticed, the greater damage was on the top tube, not downtube. As far as I can tell, there's no indication that the frame was poorly welded at manufacture, or that the tubes were defective; it just had a massive impact after about 6,000 miles or so.

The LHT has pretty beefy and slightly ovalized tubes, so I doubt using a different frame on that trip would have made much of a difference.

Also, keep in mind that many of the posters here are using that same frame without any problems. One single frame with a failure like that is hardly evidence of rampant frame failure, either for that frame model in particular or for touring bikes in general.

Independent Fabrications' touring bikes have been built with reinforced downtubes. The designer said that he had seen too many frame failures on the downtube, near the juncture with the head tube -- he had seen this enough times to warrant reinforcing the area. The top tube is also reinforced near the headtube.

Could you elaborate on how exactly the DT-HT and TT-HT joints are reinforced? I looked at the bike on the IF website and didn't see anything other than a tig welded joint. Does IF just use thicker DT and HT tubes? Do they have an inner sleeve at the joint like the old Schwinn fillet brazed frames?

One obvious way to reinforce a joint is to build with lugs. Well made lugged joints are incredibly strong and stiff -- I can't imagine a DT/TT-HT joint failure except in the case of an extreme impact.

On my Surly Big Dummy and Thorn Nomad [my strongest/toughest bikes] neither has any special reinforcement at the HT- DT area. The Big Dummy has been heavily abused with not the slightest frame related issue.

Some silver ones, a black one, a red one, an orange one and a couple of titanium ones

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Originally Posted by Niles H.

Independent Fabrications' touring bikes have been built with reinforced downtubes. The designer said that he had seen too many frame failures on the downtube, near the juncture with the head tube -- he had seen this enough times to warrant reinforcing the area. The top tube is also reinforced near the headtube.

A recent thread on bikeforums.net dealt with a failure after hitting a pothole, with good pictures of the damage, and the repair job as well: Potholed, is my LHT still rideable?

Another advantage of the Independence frames is that they can be built from Reynolds 853 and other hardened steels (the fork is also made from stronger-than-usual steel). These steels have far higher yield strengths than the usual, non-hardened steels (and some of the other materials) used in most touring bikes.

What other bikes are made of tubing or materials that are significantly less likely to fail? -- especially in collisions with curbs, potholes, rocks, and other objects that cause these sorts of damage and failures?

Can a non-reinforced bike be reinforced after purchase?

Adding a gusset to a mountain bike frame under the downtube a the headtube/downtube joint is fairly standard practice. It's a pretty easy way of beefing up the joint without adding too much weight. Here's a couple of images

The first one on the Chromag frame is a fairly simple gusset and was the most commonly used one about 15 years ago.

The Mongoose gusset is probably for a bike that is more downhill or freeride oriented.

The green bike is a waaaaay over the top gusset for a double crown, jump off cliffs, fall off buildings bike.

None of these are needed for normal touring bikes. Even BF123's epic crash in China wouldn't have been helped by a gusset. His frame bent further back at the middle of the butted tube. Under normal circumstances, a touring bike is very strong and will take a lot of punishment. Not jump off cliffs punishment or falling into sink hole punishment but under normal riding, the frame will take a whole lot.

Some silver ones, a black one, a red one, an orange one and a couple of titanium ones

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Originally Posted by LeeG

isn't butted tubing a form of reinforcement?

Sort of but not quite. Tubing for bicycles doesn't have to be that thick to carry the rather tiny loads we put on bikes. By itself, the thinnest part of the tube on a bike would do fine to keep the bike from falling apart under us. However, joining thin tubing is difficult since it's easy to burn through the thin metal so you need something to keep the heat of welding or brazing from damaging the thin parts of the tube. You do this by adding weight at the ends of the tubes. As an added benefit, you add strength at the points where most of the forces that a bike experiences that will bend or break it take place.

BF123 experienced the problem of thin tubing during his repairs. Even a skilled welder has difficulty welding thin bicycle tubing. I have a machinist friend who is a master welder. He does pressure vessels that can carry hundred of pounds of pressure without exploding and he says that doing bike welding is by far the toughest stuff welding he's ever done.

it seems to me that one can simply make the tubing a bit heavier than is needed for welding and normal riding and you've effectively "reinforced" it. Basically it's a point of semantics, the design can be built for extreme stresses if the tubing is available

Even a skilled welder has difficulty welding thin bicycle tubing. I have a machinist friend who is a master welder. He does pressure vessels that can carry hundred of pounds of pressure without exploding and he says that doing bike welding is by far the toughest stuff welding he's ever done.

thirty years ago I had a custom frame built up by a local builder, it was an eye opener watching him replace a damaged tube on a customers bike. He handed me some goggles to watch the process. In the following years I saw a few guys get into frame building and offer their frames to local racers,,and have those frames fail underneath them. One time I was watching a cyclocross race where a guy had the top tube pull out of a head tube lug while traversing a bumpy field.

There's an old axiom in design/engineering that goes" light, strong , cheap, you can have any two of the three".You can re enforce anything. Build the frame out of thick wall tubing, it will weigh maybe 10 kilo's, but be very strong. Then a wheel or fork will deform instead. You pays your money and you takes your chances.In the grand scheme of things in the touring world, I think frame failures are way down the list of things that go wrong.
Cheers